1. Field of the Invention
The present invention relates to a clutch device used in an automatic transmission for an automobile.
2. Description of the Related Art
In an automatic transmission used in an automobile, a multiple disc wet-type clutch device, comprising plural clutch discs and separator plates which are engaged with each other by the pushing force of a piston which is driven by oil pressure, is commonly used.
In such a type of clutch device, it is necessary to increase the oil pressure or to increase the number of clutch discs and separator plates to attain higher torque transmitting capacity.
However, it is impossible to attain an oil pressure which is higher than line pressure which is generated by an oil pump, and it causes an increase of axial length if the number of clutch discs and separator plates is increased.
Therefore, a clutch device which is provided with a cam mechanism between the piston and one of clutch disc or separator plates has been developed (Japanese Unexamined Utility Model Publication (KOKAI) No. 2-69134).
In the above type of clutch, cam members are separated when the piston begins the operation, so that clutch and separator plates are suddenly engaged and this causes a shock.